The development of the radio-mobile telecommunications market and the ever more wide-spread use of personal communication devices and communication between machines, known as M2M (Machine-to-Machine), make the supply of services for mobility control more and more economical. Furthermore, the introduction of packet transmission services such as those provided by the radio-mobile network of the GSM (2G), UMTS(3G) and the like, by ensuring constant connectivity to the communication network, at the same time makes the localization services more and more efficient and accessible.
A first known category of localization and mobility control methods consists of “network based” methods. These methods provide to process measurements made on predetermined physical values of the radio electric signal, detected by a mobile radio terminal and by the mobile telephone network. E-OTD (Enhanced Observed Time Difference), TDOA (Time Difference of Arrival), AFLT (Advanced Forward Link Trilateration) and Cell-ID all belong to this category.
All methods of the first known category require an active support by the network that shall be involved to provide broadcasted information on the network geographical structure or to provide positioning estimation services based on mobile station performed measurements.
In particular, E-OTD, TDOA Downlink and AFLT are based on the accurate measurement of the delay in propagation of a specific signal transmitted by a constellation of base radio stations, also known as cells, of known geographical position, and received by the mobile radio terminal, the position of which is calculated by triangulation.
TDOA uplink is also based on a triangulation calculation: in this case the measurement is made on the delay with which the signal transmitted by the mobile radio terminal is received by at least three base radio stations.
Cell-ID, on the contrary, is based on a parameter of the mobile radio network transmitted by each base radio station in order to allow the univocal identification of a determinate geographical area. In this case the geographical localization is indicative of the area covered by the base radio station.
An example of “network based” method is described in WO 96/35306 in which a mobile unit, namely a cell phone, calculates its own geographical position, on the basis of the measurements of time differences of predetermined service signals received by the mobile unit from at least four Base Transceiver Stations, or BTS, serving the mobile unit itself. In order to calculate its own geographical position, the mobile unit must also know the exact geographical position of serving BTS stations. This is carried out by sending at least a specific message, such as an SMS (Short Message Service), to mobile units, said message containing at least data related to the exact geographical position of the serving BTS stations. This message should be broadcasted at a predetermined time rate so as to allow each mobile unit to calculate its own position.
One disadvantage of network-based methods is that the localization service is carried out by the company that manages the mobile telephone network, and that it implies a rather considerable use of radio resources. For example, the impact of the localization service traffic may not be negligible compared with the normal network traffic. This requires an increase in the network resources in order to maintain the desired quality of service at predetermined levels, and a consequent increase in the costs of managing the network infrastructure. On the contrary there may also be a deterioration of the localization service, especially when the service is widely diffused and in highly urbanized areas. Furthermore, these localization methods are guaranteed in a specific national area, whereas they may not be usable abroad, since they are connected to specific services supplied by particular network operators.
There is a second category of known localization and mobility control methods called mobile-based, or satellite based, methods. These are substantially autonomous from the network in calculating position. One method is based on GNSS technology (Global Navigation Satellite System) of which GPS (Global Position System) is the most widespread.
GNSS is based on a triangulation principle which, measuring the difference in the propagation delay of a signal emitted by a constellation of satellites orbiting the Earth, and received by a generic device, calculates with great precision the geographical coordinates thereof.
One disadvantage of mobile based methods is that the cover of the unidirectional signal transmitted by the satellites is not always constant, since, while the cover of the signal is substantially guaranteed in the open, such as in the countryside or at sea, it fails in areas inside houses and in highly urbanized areas, where the presence of tall buildings makes it impossible to see the minimum number of satellites needed to calculate triangulation.
Another disadvantage is due to the high electric consumption of the GNSS receiver, which is in any case higher than the electric consumption of a mobile terminal in inactive condition. This entails a considerable decrease in the operating autonomy of the batteries.
One purpose of the present invention is to achieve an improved localization and mobility control method, applicable to a mobile radio terminal served by a mobile telephone network, which allows the absolute or relative localization of the terminal, or a person or object associated with said terminal, in an autonomous manner and without the network being aware.
Another purpose of the present invention is to achieve an improved localization and mobility control method which allows a minimum energy consumption for mobile terminals.
Another purpose is to achieve a localization and mobility control method, which allows localization in every operative condition.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.